Mike,

I pulled the steering wheel nut from my 85 yesterday and also found it
to be smaller than the 18 x 1.5 of the O2 sensor and larger than a 14 mm
spark plug and concluded it was a for a 16 mm thread pattern.

And I have also seen the outer nut size for the Vanagon steering wheel
nut consistently reported as needing a 24mm socket.

Sam

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Sam Walters

Baltimore, MD